Abstract We developed a high-speed image reduction pipeline using Graphics Processing Units (GPUs) as hardware accelerators. Astronomers desire to detect the emission measure counterpart of gravitational-wave sources as soon as possible and to share in the systematic follow-up observation. Therefore, high-speed image processing is important. We developed a new image-reduction pipeline for our robotic telescope system, which uses a GPU via the Python package CuPy for high-speed image processing. As a result, the new pipeline has increased in processing speed by more than 40 times compared with the current one, while maintaining the same functions.